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Now let's suppose that we are giving alcoholic drinks to two identical twins. These twins were not only born identical, they also lived identical lives, even down to eating the same food and having identical exercise programs — so they have identical weights. In our little hypothetical experiment, the twins are perfect controls for each other.

The plan is to give them a couple of mixed alcoholic drinks, and yes, with the same amount of alcohol. But here's the only difference. One twin gets normal soft drink, with about 45 grams of sugar, as the mixer. The other twin has the same brand of soft drink, but without the sugar — that is, with a zero calorie artificial sweetener.

Driving home in their two identical cars, they both get tested for blood alcohol level thanks to a police random breath test check. (The police don't have to be identical twins, but the breath testing units are — that's science and engineering for you.)

The result is amazing. The twin who drank alcohol mixed with the sugared soft drink is legal — his blood alcohol comes in at 0.034, well under the limit. But the twin who drank exactly the same amount of alcohol, but mixed with the zero calorie artificial sweetener is measured at 0.053. He's just over the limit, and it's off to 'The Cooler' for him.

What's going on? How can they have different blood alcohol levels if they drank exactly the same amount of alcohol?

It's all due to a single fact.

Your stomach will push out its contents into the next section of the gut, the small intestine, at what is pretty well a fixed rate. It's about 8-12 kilojoules per minute. The food in the stomach just has to wait until the food before it has gone ahead. In other words, the presence of food in your stomach will delay or slow down how quickly your stomach empties. Alcohol with added sugar takes longer to move along than alcohol alone (that is, without any extra calories).

In one study at Royal Adelaide Hospital, the volunteers drank 30 grams of alcohol, or about three so-called standard drinks. The energy content was about 942 kilojoules.

One group had their alcohol mixed with a zero calorie artificial sweetener — so the total energy content was still the same. The stomach could push about half of this load into the small intestine in about 15 minutes.

But the other group had a regular fully-sugarised version of the alcohol. The total energy content was more than doubled to about 2,000 kilojoules. With this extra energy to deal with, the stomach took about 21 minutes to push half of its load into the small intestine. During that extra time, it seems that some of the alcohol was broken down (or destroyed) in the harsh and hostile acid environment of the stomach.

As a result, there was less alcohol left to be pushed into the small intestine, from where it would get absorbed. The peak blood alcohol level was less — which is why one hypothetical twin was under the legal limit, and the other one, over it.

The vast majority of us (and that includes me) have had no idea that, for example, a rum with diet cola would get you drunker than a rum with regular cola. And yes, this turns out to be part of the essential knowledge you need to survive in our Western society. Here, alcohol is more or less all-pervasive, being present at most social occasions.

Now that you know that diet mixed drinks get you drunker, you should try to use this information for good. After all, as Mary Poppins said: "A spoonful of sugar helps the medicine go down."